The use of nonlinear device behavioral models offers an economical way of simulating the performance of complex communication systems. A concrete method for implementing the AM/AM AM/PM behavioral model in system level simulation using ADS is developed. This method seamlessly tansfers the data from the circuit level simulation to system level simulation, where the AM/AM AM/PM model is automatically built. The methodology is extendible for use in other software packages or between different software packages

Shen, Y.

Tauritz, J.L.

English

The use of nonlinear device behavioral models offers an economical way of simulating the performance of complex communication systems. A concrete method for implementing the M A M AMPM behavioral model in system level simulation using ADS is developed. This method seamlessly tansfers the data from the circuit level simulation to system level simulation, where the AWAM AM/F'M model is automatically built. The methodology is extendible for use in other software packages or between different software packages

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On the implementation of AM/AM AM/PM behavioral models in system level simulation

University of Twente Research Information

On the Implementation of AMAM AMPM Behavioral Models in System Level Simulation Y. Shen and J.L. Tauritz Microwave Techniques Group, Telecommunications Engineering UNIVERSITY OF TWENTE 7500 AE ENSCHEDE, NETHERLANDS Abstract: The use of nonlinear device behavioral models offers an economical way of simulating the performance of complex communication systems. A concrete method for implementing the M A M  AMPM behavioral model in system level simulation using ADS is developed. This method seamlessly tansfers the data from the circuit level simulation to system level simulation, where the AWAM AM/F'M model is automatically built. The methodology is extendible for use in other software packages or between different software packages. I. INTRODUCTION 'Ihe MAM AM/PM behavioral model is the lowpass equivalent representation of a microwave nonlinear device/system. Since sampling the high frequency carrier to compute the output waveform is avoided, it drastically reduces the time required for the simulation Normally speaking, a simulation program that evaluates wireless system specifications such as ACPR and EVM consists of two parts, i.e., the circuit level simulation where the data for building the behavioral model of the nonlinear devicekystem is generated, and the baseband system level blocks that characterize the rest of the system ['I. Automatic background linking of the different level simulations is preferable in that any modification to the circuit side can reveal its impact simultaneously on the system side. Although dozens of papers have been devoted to the extraction of the behavioral model of the nonlinear device, an efficient way of implementing the behavioral model in the baseband system level simulation does not appear to have been reported. In [2] ,  we demonstrated that the AWAM AM/F'M model is accurate for a quask static nonlinearity. This paves the way for use of a common interpolation algorithm in the model building. A natural conclusion is that when the number of sampling points increases, the answers converge independent of the interpolation method chosen. Contemporary Harmonic Balance (HB) simulation is mature and efficient so that increasing the number of points of a single tone HB simulation adds little cost to the task while gaining both improved accuracy in system simulations as well as flexibility in the realization of library components. In our proposed method, piece-wise linear interpolation is used. Results are compared with those from cubic spline interpolation in section 111. 0-7803-7143-7/02/$10.00 2002 IEEE. 111 Authorized licensed use limited to: UNIVERSITEIT TWENTE. Downloaded on September 2, 2009 at 14:50 from IEEE Xplore.  Restrictions apply. Behavioral models do exist in the libraries of commercial software such as Agilent EEsof s ADS. In the case of power amplifiers, when using ADS, they are the "RF System Amplifier" in "Analog/RF Network" and "GainRF" in "Digital Signal Processing Network" 13]. "RF System Amplifier'' is an AM-AM AM-,PM database model, but its usage is limited to the field of analog simulation so that integration into purely baseband system level simulation is difficult. On the other hand, the input- output relationship of the "GainRF" block is: c,,, *V,"(f)I (1) v,,(t)=I",.(t)le'",,, where: a is the linear gain and gomp the gain compressbn factor. Although "GainRF" is a block that can be used in baseband systemlevel simulation, it is not the M A M  A W M  model we need. In section I1 a concrete method is described for automatically building the lowpass equivalent MAM AMPM model in ADS system level simulation. To do so, the data from the circuit-level simulation is transferred to the system level simulation via a temporary data file. Data interfaces are built at both simulation levels. Simulation programs realized in this way have, in practice, been found to be user friendly and economical to maintain and update. The method is extendible for implementation in other software packages or between different software packages. It is also a good candidate for more advanced behavioral model implementations, such as in frequency dependant models. II. Proposed Implementation Fig. 1 shows the basic structure of the proposed method. We note that the scheme consists of three parts. The first is at the circuit level, with the HJ3 simulator as the simulation controller, the second is at the system level, with the digital Ptolemy simulator as the simulation controller, the third is basically a data file that transfers all the information necessary to build the behavioral model linking circuit level simulation to system level simulation. Fig.1 also illustrates the need for building interfaces to write data into the data file and read data out of it. Fig.2 and Fig.3 show additional details related to circuit level and system level simulations, respectively. The data interface for the circuit level simulationis realized with a 'MeasEqn' component, in combination with user defined Application Extension Language (AEL) routines. Fig.3 is a block diagram of the system level simulation. Details of the implicit data interface hidden under the behavioral model BM are shown in Fig. 4. Retrieval of data from the data file and implementation of piece-wise linear interpolation are tasks in "GainRF", the behavioral model in the digital library. Since this model doesn't directly provide AWAM and AM/PM data, a schematic like that shown in Fig. 4 is necessary in order to build the quashtatic model. III. Simulation results I12 Authorized licensed use limited to: UNIVERSITEIT TWENTE. Downloaded on September 2, 2009 at 14:50 from IEEE Xplore.  Restrictions apply. Using the approach explained in the last section, we have obtained results similar to those from other interpolation methods 14', i.e., good correlations with the results of harmonic balance simulations have been found up to IMD9. In addition comparison with the results from circuit envelope simulation is shown in Fig 5 .  EVM results, at moderate sampling density, using both piece-wise linear and cubic spline interpolation are given out in Table I. IV. Conclusions Consistent with our latest theoretical research, no performance deterioration will be experienced with AMAM AM/PM model if the mdeled nonlinearity is quasi-static and the input signal is narrowband. Using this result, a concrete method for automatically building the AWAM AM/PM model in ADS system level simulation is proposed. Realization details are presented and the simulation results confirm the theory. Seamlessly linking both circuit level and system level simulation, this method is particularly suited for establishing a friendly design environment facilitating cooperation between system and circuit engineers. The principle ckpicted in Fig. 1 can be applied in other software packages or between different software packages. One of our following research goals is adaptation of the model for frequency dependance, and for nonlinearities with memory effects if possible. REFERENCES [ I ]  J. S. Kenn [2] [3] Agilent Technologies, ADS 2002 help manual. [4] J. Staudinger, "Applying the Quadrature Modeling Technique to Wireless Power Amplifiers," Microwave Joumal, Vol. 40, No. 11, pp. 66-86, Nov. 1997. and A. Leke, "Power Amplifier Spectral Regrowth For Digital Cellular andi'PCS Applications," Microwave Journal, Vol. 38, No. 10, pp. 74-92, Oct. 1995. Quasi- Static Bandpass Nonlinearitie s Usin Volterra Series,'' 60' ARFTG Conference, Washington, D.C., Dec. 5-6,ZOOf Y.Shen, and J. Tauritz, "On the Analysis of Fig. 1 Method of linking circuit simulation and system simulation 113 Authorized licensed use limited to: UNIVERSITEIT TWENTE. Downloaded on September 2, 2009 at 14:50 from IEEE Xplore.  Restrictions apply. Interface I : User - defined-MeasEqn(Vin,Vout) One Tone Swept power Soice Nonlinear DeuicelSMem 1 Harmonic Balaiiace I Fig. 2 Circuit level simulation Digital Source Band Limiting Filter ~ Condellation IEI & EVM Fig. 3 System level simulation Interface I /  Fig. 4 The AMAM AM/PM behavioral model implemented in ADS I14 Authorized licensed use limited to: UNIVERSITEIT TWENTE. Downloaded on September 2, 2009 at 14:50 from IEEE Xplore.  Restrictions apply. :i 2s l 3  3; .. .*' .. ... .. . ,~ .. . .. ..... i~ . . . . . . . . ,  .............. : ..... : i ",_- ~ l".." io It 23 " ,i J :/m i,m Fig. 5 Comparison with results from circuit envelope simulation Table I: EVM based on piece wise linear and cubic spline interpolatio; 1 Datal1 I Relative 0 Data I: cubic spline interpolation Data 11: piece wise linear interpolation (moderate sampling density) 115 Authorized licensed use limited to: UNIVERSITEIT TWENTE. Downloaded on September 2, 2009 at 14:50 from IEEE Xplore.  Restrictions apply. 

Applying the Quadrature Modeling Technique to Wireless Power Amplifiers,&quot;

https://doi.org/10.1109/ARFTGS.2003.1216874

On the Implementation of AM/AM AM/PM Behavioral Models in System Level Simulation

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